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Table 1. Representative Rates at Which Heat and Moisture Are Given Off by Human Beings in Different States of Activity.

Copyright © 2007, American Society of Heating, Refrigeration and Air-Conditioning Engineers, It is presented for educational purposes only. This table may not be copied and/or distributed electronically or in paper from without permission of ASHRAE

At rest, over 50% of the sensible heat transfer between the occupant and the room is radiant based - and yet 99.99% of all thermostats measure air temperature - go figure.

Visit our radiant design and performance characteristics page.

Radiant Based HVAC Systems

Many people assume wrongly that Radiant Based HVAC Systems are mechanical or electrical solutions like floor heating.

However, 'radiant' control is ideally first an architectural solution.

This means the built environment should be the prime solution for controlling the radiant exchange between the occupant and the interior surfaces.  This is achieved with building efficiency.  The higher the performance in the building envelope the less temperature difference between the person and the room mass the more comfortable the occupant.  This begins to occur when loads are reduced with architectural systems to less than 12 Btu/hr/sf.*  Mechanical solutions, if necessary, are then applied to compensate for the buildings short comings. 

Therefore, when we use the term Radiant Based HVAC Systems, please understand we are talking about the body’s radiant heat transfer to and from the built environment (see Table 1.) and controlling it first with architecture then with mechanical solutions.

As illustrated below, low performing buildings using traditional heating systems need high fluid temperatures in heating (and low temperatures in cooling) but only a high performance building can use low temperatures in heating and high temperatures in cooling. In fact with high performing buildings, using radiant cooling and heating, conductive floors and close tube spacing, fluid and surface temperatures operate close to the core body temperature.

click to enlarge

Such a small difference between the fluid temperatures in the pipes and the fluid temperature in your blood has a major benefit in that it greatly enhance the efficiency of chillers, condensing boilers, solar and heat pumps. So you win when you improve the building and you win if/when you use radiant heating and cooling.

To see an example of a high performance building with radiant heating and HRV's for ventilation click here.

If you wish to discuss this further please visit the Online Help.

Radiant Based HVAC – What does it mean to indoor air quality?

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*To put this into perspective, Passivhaus protocol establishes < 4 Btu/hr/sf loads. At such low fluxes there is little need for heating of any type.